There’s an article at NewsForge about Linux on Motorola cell phones and the lack of native applications:
The big question is, what does Motorola gain by obstructing willing developers from bringing software to their platform?
Actually, it’s not that much of a question, the answer is just a bit higher up in the article: they gain carrier approval. Carriers view open platforms as a threat to their business model. This is one of the reasons for the newer versions of Symbian including a signing infrastructure as part of the OS. This actually represents a move away from the open platform approach they have. It does nothing for the user, and nothing for the device manufacturer. All it really does is increase the friction in terms of getting an application onto a handset, which benefits the carrier who wants to take a cut of any application install (because of course they want to drive folks to their deck instead of installing apps on their own).